Transfer of xerographic dye images



TRANSFER OF XEROGRAPHIC DYE IMAGES Filed Feb. 2, 1959 INVENTOR. Jerry N. Martin A TTORNE Y 3,060,052 TRANSFER OF XEROGRAPl-HC DYE IMAGES Jerry N. Martin, Columbus, Ohio, assignor, by means assignments, to Xerox Corporation, a corporation of New York Filed Feb. 2, 1959, Ser. No. 790,639 5 Claims. (Cl. 11.7-17.5)

This invention relates to Xerography and more particularly to the transfer of Xerographic dye images.

In a usual form of xerography, an electrostatic latent image is formed on the normally insulating surface of a Xerographic plate and this charge pattern is then made visible by selective deposition thereon of finely divided electrostatically attractable powder particles. These particles commonly comprise finely divided particles of pigmented synthetic resins, finely divided carbon, minerals, pigments, etc. The powder image is then customarily transferred to another support, such as a sheet of paper, for examination. in another form of Xerography with which the present application is concerned, electrostatic charge patterns are developed or made visible by the deposition of finely divided particles of water soluble dyes. The development operation, which is not itself a part of the present invention, may be carried out in a number of ways, such as through cascade development, aerosol development, or the like, and results in a dry dye image deposit on the charge pattern bearing surface. Various forms of normally insulating layers are known for use in xerographic plates, including, but not limited to, vitreous materials, such as vitreous selenium, as well as dispersions of photoconductive pigments in insulating resin binders. In substantially every case, and in every case in which this invention is applicable, the normally insulating layer which carried the electrostatic charge pattern and which is developed by the dye particles is, in a practical sense, insoluble in and impermeable to water.

It has been customary to transfer such xerographic dye images to an image support comprising a layer of hardened gelatin generally containing a mordant and coated upon a suitable mechanical support base. The hardened gelatin layer may be replaced by other slightly water permeable materials having similar physical properties, such as other natural or synthetic colloids. This gelatin type of material is preferred because of the density and intensity of dye images attainable thereon as compared with other possible materials, such as ordinary paper. A suitable commercial product of this type is available from the Eastman Kodak Company, Rochester, New York, under the name dye transfer paper and generally comprises a sheet of white paper coated with a layer of hardened gelatin containing a mordant. The image receiving member will be referred to throughout this specification as dye transfer paper without any intent to be limited to a particular commercial product.

The transfer of the dye image has generally been effected by soaking a sheet of dye transfer paper in water for several minutes and then partially drying the sheet by passing it through a pair of wringer rollers while sandwiched between two sheets of blotting paper or optionally between a sheet of blotting paper and a polished metal plate. This technique of preparing the dye transfer paper is fully disclosed in US. Patent 2,843,499. The sheet of dye transfer paper which is now in a damp condition, is then placed against the Xerographic plate, with its gelatin surface contacting the dye image. After a short interval on the order of several minutes, the dye transfer paper may be removed and a brilliant dye image is found to be imbibed into the gelatin layer. This transfer procedure, however, is incapable of producing high 3,060,052 Patented Oct. 23, 1962 "ice quality dye images because the denser parts of the image are invariably found to be badly mottled after transfer. It is presently believed that this mottling is due to the liberation of a small amount of free water at the surface of the dye transferpaper where it is pressed into contact with the xerographic plate, thus forming a concentrated solution of the dye which is randomly displaced before it is absorbed into the gelatin. It is also believed that in the less dense portions of the image the lesser amounts of dye are immediately absorbed by the dye transfer paper before mottling can take place. It has also been proposed that the dye cannot be diffused into the hardened gelatin surface as fast as it is solubilized, and consequently that the dye is squeezed into the small, irregularly spaced indentations on the surface of the paper to give a mottled appearance. It has been found that if the moisture content of the dye transfer paper is reduced in an attempt to avoid mottle, incomplete transfer results. Regardless of the validity of the proposed theoretical explanations, it has not heretofore been possible to transfer onto dye transfer paper Xerographic dye images without mottle and having both high quality and high density.

In co-pending application Serial No. 774,847, dated November 19, 1958, issued October 10, 1961, and bearing Patent No. 3,003,891, there is described a method for producing unmottled dye images on dye transfer paper through a process involving two separate transfer or inbibition steps. I have now found, however, new means and methods which permit the production of unmottled brilliant dye images in a single operation. I accomplish this through the addition to a conventional type of dye transfer paper of a thin overcoating of a soft, highly Water permeable material.

The accompanying figure is a schematic cross-sectional view of such an overcoated image support material according to the invention.

In the drawing, element 10 is a conventional support layer such as a sheet of white paper and element 11 is a layer comprising hardened gelatin or other colloid, generally containing a mordant, and coated on element 10. Thus, elements 10 and 11 alone comprise the conventional dye transfer paper of the prior art. Element 12 is a thin layer of soft water permeable material coated on top of layer 11. Unhardened gelatin is a particularly useful material for forming layer 12 and will be used illustratively throughout this specification, but other natural or synthetic colloids or the like with similar physical properties may also be employed.

Assuming that conventional dye transfer paper is available, by purchase or otherwise, various conventional methods may be used for applying layer 12. According to one method, the dye transfer paper may be moistened and a 4% aqueous gelatin solution sprayed onto it. This generally produces a coating thickness of about 3 to 8 microns depending on the techniques employed. A second method is to soak the dye transfer paper in an 8% aqueous gelatin solution at 25 C. for about 2 minutes after which the paper is removed and allowed to drain. The presently preferred method involves running a web of dye transfer paper through the conventional type of coating machine generally used to apply the photosensitive emulsion to photographic enlarging paper. In this type of machine one face of a moving web is momentarily brought into contact with or wetted by a surface of a body of coating liquid maintained in a trough of coating material. With this type of machine a gelatin solution of at least 6% should be used, as lesser concentrations generally yield a coating which is too thin for the purposes of this invention. A gelatin solution of about 10% appears to give the best results while a 14% solution yields coatings which are too thick, which swell excessively and which are too easily damaged.

It is generally preferred to specify the thickness of layer '12 in'terms of the concentration of the gelatin solution from which it is coated, since it is very difiicult to make a'direct, accurate physical measurement of thin gelatin layers.

It is necessary'to thoroughly dry or cure layer 12 in order to secure adequate adhesion to layer 11. if layer 12 is not adequately dried, it tends to peel olf layer 11 when the overcoated dye transfer paper is subsequently soaked in water. An air drying time of at least 5 days will prevent such peeling as will a forced drying at 200 F. for atleast 30 minutes.

The overcoated dye transfer paper of this invention must be moistened before use, and substantially the same techniques previously described for moistening conventional'dye transfer paper may be used. One useful technique comprises soaking the overcoated dye transfer paper in tap water for about 2 minutes and then removing it from the water, laying it face down on a smooth surface such as glass or polished metal, and rolling a blotter over the back to remove excess water. A somewhat simpler technique involves soaking the paper in tepid water at 30 C. for about 1% minutes, draining, placing the paper face up on a sheet of glass or the like and lightly drawing a squeegee over the surface. It has been found that in this latter method the squeegee removes a small amount of the thin gelatin overooating layer 12, but this does not have any adverse effect on the usefulness of the transfer paper.

' After the transfer paper has been moistened by the above or other equivalent techniques, it is then placed against the xerographic plate, with its gelatin surface contacting the dye image. Light pressure greater than about 2 and less than about 15 lbs/linear inch may be applied by a roller or platen. After a short interval of several minutes, the paper may be removed and a brilliant dye image, free from mottle, is found to be imbibed thereon. The exact role played by the unhardened gelatin coating is not clear. However, the presence of unhardened gelatin in the minute depressions in the surface of the dye transfer paper may offer areas that will quickly absorb any dye pushed toward them before they agglomerate into a dye producing pattern.

Although the present invention has heretofore been described in terms of its utility for transferring xerographically prepared dye images, it is apparent that it is equally useful for transferring dye images, however formed, from any water impermeable surface regardless of the electrical properties of that surface.

What is claimed is:

1. The method of forming a brilliant mottle-free imbibed dye image from a dry water soluble dye image residing on a water impermeable surface comprising:

(a) moistening a unitary transfer member comprising a paper sheet support layer having a. first uniform layer coated on said support layer consisting essentially of solid chemically hardened slightly water permeable gelatin and having a second uniform thin surface layer coated over said first layer consisting essentially of solid unhardened and highly Water permeable gelatin by first soaking in water and then removing excess water,

(1)) contacting said dry dye image on said water impermeable surface with the moistened surface layer of unhardened gelatin of said unitary transfer member,

(0) allowing said dye image to be absorbed into said unitary transfer member, and

(at) removing said unitary transfer member from said water impermeable surface.

2. The method of claim 1 in which said surface layer of said unitary transfer member has a thickness at least equal to that formed on a member by withdrawal of a member from an aqueous gelatin solution having a concentration of at least 6%.

3. The method of claim 1 in which excess water is removed in the moistening step by blotting.

4. The method of claim 1 in which excess water is removed in the moistening step by squeegeeing.

5. The method of claim 1 in which a roller exerting a pressure between about 2 and about 15 lbs/linear inch is rolled against said paper sheet support layer of said unitary transfer member during said contacting step.

References Cited in the file of this patent UNITED STATES PATENTS 227,629 Holtzmann May 18, 1880 542,785 'Ihuringer July 16, 1895 1,528,660 DeSperati Mar. 3, 1925 1,625,714 DeSperati Apr. 19, 1927 1,699,349 Dailey Jan. 15, 1929 1,905,438 Capstaif Apr. 25, 1933 2,038,118 MacLaurin Apr. 21, 1936 2,551,582 Carlson May 8, 1951 2,699,408 Camras Jan. 11, 1955 2,761,416 Carlson Sept. 4, 1956 2,780,560 Hanley Feb. 5, 1957 2,843,499 Andrus July 15, 1958 

1. THE METHOD OF FORMING A BRILLIANT MOTTLE-FREE IMBIBED DYE IMAGE FROM A DRY WATER SOLUBLE DYE IMAGE RESIDING ON A WATER IMPERMEABLE SURFACE COMPRISING: (A) MOSITENING A UNITARY TRANSFER MEMBER COMPRISING A PAPER SHEET SUPPORT LAYER CONSISTING ESSENLAYER COATED ON SAID SUPPORT LAYER CONSISTING ESSENTIALLY OF SOLID CHEMICALLY HARDENED SLIGHLY WATER PERMEABLE GELATIN AND HAVING A SECOND UNIFORM THIN SURFACE LAYER COATED OVER SAID FIRST LAYER CONSISTING ESSENTIALLY OF SOLID UNHARDENED AND HIGHLY WATER PERMEABLE GELATIN BY FIRST SOAKING IN WATER AND THEN REMOVING EXCESS WATER, (B) CONTACTING SAID DRY DYE IMAGE ON SAID WATER IMPERMEABLE SURFACE WITH THE MOIS TENED SURFACE LAYER OF UNHARDENED GELATIN OF SAID UNITARY TRANSFER MEMBER, (C) ALLOWING SAID DYE IMAGE TO BE ABSORBED INTO SAID UNITARY TRANSFER MEMBER, AND (D) REMOVING SAID UNITARY TRANSFER MEMBER FROM SAID WATER IMPREMEABLE SURFACE. 